There is a need for an inexpensive, effective, yet safe and convenient method to minimize the microbial burden of objects we interact with. In addition, this method must not leave behind microbes with resistance to future treatment. This need is primarily evidenced by unacceptably high rates of infection in hospitals and health care facilities. But there are also problems in daycare facilities, schools, the food industry and the travel industry, among others. Additionally, these problems are becoming more severe as microbes which are resistant to virtually all known antibiotics are becoming more common. It has been predicted that we may soon enter a post-antibiotic era that will be similar to the pre-antibiotic era in which even minor infections will be life threatening.
Consequently, a method for killing virtually all microbes is needed that prevents the microbes from developing a resistance and with ingredient compounds that are not hazardous to humans, pets and other beneficial life that may be exposed to them. A potential way to do this would be to utilize ingredients and methods that are relatively safe to humans but are biocidal.
For centuries prior to the antibiotic era, humans had safely utilized natural biocides. Vinegar has been well known to protect foodstuffs from the effect of microbes, evidenced by many foods being pickled. Ethanol has also been used for years. In Europe, for example, medieval monks who brewed and drank wine or beer instead of the local water had much longer life spans. More recently, hydrogen peroxide has been shown to be used by animals as an internal method to ward off the microbes that infest them. Additionally, electricity has a biocidal effect, as does ultraviolet light.
The problem with these safe biocides is that each one individually is not effective against all types of microbes, and several target microbes have developed defense mechanisms against these biocides. However, combinations of two or more of these biocides have proven to work synergistically to enhance each one's effects. Particularly, combining hydrogen peroxide and acetic acid (the primary component of vinegar) to form peroxyacetic acid has proven to be especially effective. Several methods, apparatuses, and disinfecting systems utilizing peracids, including peroxyacetic acid, have been described in U.S. Pat. Nos. 6,692,694; 7,351,684; 7,473,675; 7,534,756; 8,110,538; 8,696,986; 8,716,339; 8,987,331; 9,044,403; 9,050,384; 9,192,909; 9,241,483; and U.S. Patent Publications 2015/0297770 and 2014/0178249, the disclosures of which are incorporated by reference in their entireties.
However, one of the biggest drawbacks with using peracids is that they are easily hydrolyzed to produce ordinary acids and either oxygen or water. Consequently, peroxyacetic acid has limited storage stability and a short shelf life. Peroxyacetic acid instability is described in detail in U.S. Pat. No. 8,034,759, the disclosure of which is incorporated by reference in its entirety. Often, commercially available products contain additional components to combat this problem, by including either a large excess of hydrogen peroxide to drive equilibrium toward the peracid form, or stabilizers such as other acids, oxidizing agents, and surfactants. Some methods have prevented degradation during shipping and storage by requiring that individual components of a peracid composition be mixed together, and subsequently applied, at the location and time that a target will be disinfected or sterilized. Yet, these methods nonetheless require expensive additives that are difficult to obtain, such as polyhydric alcohols, esters, and transition metals, as well as specific reaction conditions, in order to be effective. In all cases, the peracid is nonetheless formed in solution and then subsequently applied to areas or surfaces that need disinfecting.
Additionally, there are known safety concerns associated with dispersing airborne particles or peracids into the environment in an effort to sterilize or disinfect it. Particularly, inhaling peracids can be dangerous, especially at the micron-level particle sizes necessary to effectively disinfect a plurality of surfaces within common inhabitable areas such as hospital rooms, hotel rooms, bathrooms, lobbies, offices, and transportation cabins. Safety data and recommended exposure levels are described in detail in Acute Exposure Guideline Levels for Selected Airborne Chemicals, National Research Council (US) Committee on Acute Exposure Guideline Levels, pg. 327-367, Volume 8, 2010, the disclosure of which is hereby incorporated by reference in its entirety.
As a result, there is still a need for sterilization and disinfecting methods utilizing peracids that are simultaneously effective, convenient, and safe, while at the same time using cheap and readily available materials.